Experience with and expectations for the drive laser for the APS PC gun

Laser Issues for Electron RF Photoinjectors, Oct. 23-25, 2002, SLAC

Experience with and expectations for the drive laser for the APS PC gun

Yuelin LiAdvance Photon Source, Argonne National Laboratory


LayoutLayout

* Current APS drive laserConfiguration, and features Problems and solutionsCurrent performances, and surprisesSummary

* Expectation for the next drive laserOperation and performance requirementSome commercial systems, new ideasAdaptive emittance optimization loopSummary

* Acknowledgement


Role of the APS pc gun drive Role of the APS pc gun drive laserlaser

1 nC0.5-10 ps

3 mm mrad200-450 MeV

LEUTL: the free electron laser projectSaturated at wavelength as short as 150 nm

100-200 fs pulses, energy 60-250 J


APS pc gun drive laserAPS pc gun drive laser

Single-shot autocorrelator

Scanning Autocorrelator

Spectrometer

Head 1 Head 1

6 Hz, 0.4 mJ @ 263 nm1.8 nm bandwidth1-10 ps pulse durationTime jitter, 2 ps spec (?)

Flash lamp-pumped Nd:Glass Chirped pulse amplification laser

BBO

Imaging aperture

Divergencecontrol


FeaturesFeaturesEnvironment Monitoring

Temperature and humidityLaser monitoring

Oscillator Energy (off line), pulse duration (off line), mode,

spectrum, AmplifierCavity buildup, mode, pulse duration, FROG (offline)

UVEnergy, mode, virtual cathode

Laser controlOff line: Pulse duration, divergence, spot size on VCOn line: Pulse energy, trajectory Semi automatic cathode cleaning


FROG traces of the laserFROG traces of the laser

Raw Reconstructed


Semi automatic cathode Semi automatic cathode cleaningcleaning

Before

After


Problems and solutionsProblems and solutions

Poor beam profilemode inhomogenityhigher order mode

Poor pointing stability50% rms

Poor outputup to 50% rmsnot enough energy

Poor reliabilitymechanical broken rodsoptical damage

Intense maintenance

•Replacing KDP with BBO•Adding pinholes at both end of the cavity•Sealing the transport line•Imaging

•Imaging•Sealing the transport line

•Replacing stretcher-compressor gratings(From originally unknown 1800 l/mm, 76% efficiency to JY 1740 l/mm, 90% efficiency)

•Scheduling flash lamp replacement•Switching cathode from Cu to Mg

•Switching Kigre rods to Schott rods•Adding pinholes to cavity

•Hiring a baby sitter


IR Spatial ProfileIR Spatial Profile

x=1.14 mmy=0.79 mm

30-40 mW @ 6 Hz

4

3

2

1

0

50 100

0 1 2 3 4 5 6

50

100


Virtual cathode imagesVirtual cathode images

4

3

2

1

0

50 100

0 1 2 3 4 5 6

50

100

Size: variableProfile: 30% flat top Pointing stability: ~2%

0 1 2 3 4 5 6

50

100

4

3

2

1

0

50 100

Direct beam

Hard edge image


Frequency conversionFrequency conversionThe power in the second harmonics at matched phase is (with pump depletion)

I

cnn

dL

L

L

P

P

effNL

NL

22

20

22

2

4

1

tanh

2.01.67491.67490.527FHG

1.91.65511.65511.053SHG

deff (pm/v)nnm

2/14

2/12

)/(

3443

)/(

6913

APL

APL

NL

NL

For BBO, type I critical phase match

At low intensityP4P

4

At high intensityP4P


Frequency conversionFrequency conversion

Expected Conversion efficiency

MeasuredGreen/IR 53%UV/green 20%

0.0732 Wavelength bandwidth (nm cm)

4.0 51 Temperature bandwidth (K cm)

0.160.53 Angular acceptance (mrad cm)

0.532 m1.064 m

UV/Green

Green/IRO

ld g

rati

ngs

New

gra

ting

s


UV Energy stabilityUV Energy stabilityLamps at 10 million shots

-0.20 -0.15 -0.10 -0.05 0.00 0.05 0.10 0.150

200

400

600

800

1000

1200

1400

Co

un

ts

E/<E>-1

15.0 15.5 16.0 16.50

50

100

150

200

20020927

<E>=208 J

E/<E>=4.3%

En

erg

y (

J)

Hours

Lamps at 1 million shots

-0.20 -0.15 -0.10 -0.05 0.00 0.05 0.10 0.150

500

1000

1500

2000

Co

un

ts

E/<E>-1

1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.60

2

4

6

8

10

20021012

<E>=9.68 J

E/<E>=1.7%

En

erg

y (

J)

Hours


Surprise: Timing stabilitySurprise: Timing stability

119 MHz rf waveform Laser rf waveform

Laser rising edge

171 ps p-p, 19 ps rmsLaser falling edge

56 ps p-p, 7 ps rms

Laser oscillator TBWP GLX-200 oscillator at 119 MHzLock device TBWP CLX-1000 timing stabilizer with spec <2 psRF source Gigatronics 2856 MHz/24 orCrystal oscillator 119 MHz


Summary on current laserSummary on current laser

* Finally usable in stability and profile

However: it is stretching its limit ….

* Flash lamps age quickly 10 million shots is the margin we use now

3-weeks of 24-7 operation at 6 HzNeeds careful attention for stable operation at the end

* Laser rods break at about 15 million shots or less Time consumingChanges laser characteristics: divergence, mode size, optical path, etc….

• No room for further improvementEnergy stability, reliability, etc..


Time to dream for a new drive laser


The future APS drive laser The future APS drive laser

Role

Primary electron beam source for both LEUTL and APS in routine operation (LEUTL is becoming a user facility)

Key operational requirement

Turn key systemReliable: no break down during normal operationStable over long timeMinimum maintenanceDeliver up to 5 nC per shot for injection to APS


The role of cathodesThe role of cathodes

Cathode (Egap+ EA)/eV Q.E. (263nm) LifeLaser energy/nC

Cu 4.5-5.6 eV210-6 (APS)310-5 (Nguyen, LANL)410-5 (GTF)

Long2.4 mJ160 J120 J

Mg3.78 eV

1.310-4 (Spring-8)1.310-3 (APS)310-3 (Nguyen, LANL)

Long36 J3.6 J1.6 J

Cs2Te 3.5 eV5% (Nguyen, LANL)1% (FNAL)

Months

CsI 6.4 eV Est. 10-3 Long

K2CsSb 2.1 eV 10% Hours

Cs3Sb 2.05 eV 6% Unstable


Laser: Dream vs realityLaser: Dream vs reality

Current Dream Reality

Pulse energy on cathode a <500 J 100 J Pulse repetition rate b 6 Hz 60 Hz Energy stability 2% rms 0.5% rms

5-10% p-p 2% p-p Pulse length 2-10 ps 2-10 ps Pulse shaping Possible Y R&D neededProfile shaping Semi Y R&D neededSpatial homogeneity 50% 10% R&D neededPointing stability 1-5% rms 1% p-p R&D neededTiming jitter to rf 6 ps rms <0.5 ps Demonstrated

(2 ps spec)Advanced features Active hydrothermal control N Y Automatic energy control Possible Y Automatic emittance optimization N YYY R&D needed

a. Based on APS QE for a Mg cathode of about 1.310-3, for 1 nC of charge from the gun.

b. With long life cathode, single pulse per rf cycle. For a SC rf with higher duty factor the requirement is different.


Commercial Ti:Sa amplifier Commercial Ti:Sa amplifier systemssystemsAdvertised performancesMake and model Rep rate Energy Stability Mode

Clark MXR, CPA-2010 0.2-2 kHz, >0.6 mJ, 1% TM00(Built in active hydrothermal Stabilization)

Spectra Physics, Spitfire 1-5 KHz 0.7 mJ 1% (p-p) TM00, 1.5 diffraction limitSpectra Physics, Hurricane 1-5 KHz 0.7 mJ 1.5% (p-p) TM00, 1.5 diffraction limitFemto Lasers, FemtoPower 1 kHz 0.8 mJ 2% (p-p) TM00, 2 diffraction limitCoherent RegA9000 300 kHz 4 J 2% (p-p) TM00, 2 diffraction limit

Energy stability <1.5% p-p, 0.24% rms @ 1k Hz (http://www.poslight.com/)

Performance ExampleSpectra Physics-Positive Light Hurricane


An idea: Gain less amplifierAn idea: Gain less amplifier

Seed: high rep, low energy pulsesf, Es Cavity with length matching

the rep rate of the seed, L=1/f

Low rep outputEout=nEs=Es/loss

AdvantagesUltra stable: Eout=n<Es>Linear device: easier to shapeLow jitter: no jitter between seed and output

Jones and Ye, Opt Lett 27, 1848 (2002)

Example: 300 mW, 100 MHz, for loss=10-4, Eout=30 J @100 kHz


Commercial lockable oscillatorsCommercial lockable oscillators

Make and model rep rate jitter spec

TBWP TIGER 200/CLX1100 up to 150 MHz <1 psFemto Laser Femto Source/Femtolock up to 150 MHz <1 psSpectra-Physics Lok-to-Clock Tsunami up to 100 MHz <1 psCoherent Mir Synchro-Lock up to 100 MHz <2 ps

Advertised performance

Laser TBWP TIGER 200 oscillator at 119 MHzLocking TBWP CLX1100RF source HP 8665B at 119 MHz

Test results 8 ps

“Subfemtosecond timing jitter between two independent, actively synchronized, mode locked lasers”

Shelton et al, Opt Lett 27, 312 (2002)


Adaptive pulse manipulationAdaptive pulse manipulation

Single shot Emittance measurement

Transverse profile measurement

Deformable mirror

Laser Electron beam

SLM pulse shaper

Single shot longitudinal profile measurement

Longitudinal and transver profile control


Measurement techniquesMeasurement techniques

Laser longitudinal profileFROG is the choice

in IR, green, SHGin UV, Polarization gating

Single-shot emittance measurementMulti slit mask

FROG example


SummarySummary

Laser

Laser technology is mature enough for the basic requirement

Advanced features

R&D is needed to adapt existing adaptive pulse shaping and waveform control technologies


AcknowledgementAcknowledgement

Gil Travish (former laser commander)Ned Arnold Sandra Biedron Arthur

GrelickMike Hahne Kathy Harkay Rich

KodenhovenRobert Laird John Lewellen Greg

Markovich Stephen Milton Antothny PetrylaSupported by the U. S. Department of Energy, Office

of Basic Energy Sciences

Contract No. W-31-109-ENG-38

Documents

Experience with and expectations for the drive laser for the APS PC gun